#include <stdio.h>

int main()
{
	int N;
	float i, a =1,b = 1,s,sum = 0;
	scanf("%d",&N);
	for(i = 0;i < N;i++)
      {
      	s = a + b;
      	a = b;
      	b = s;
      	sum = sum+b/a;
	  }
	 printf("%0.2f\n",sum);
     return 0;
 } 
 
